The present invention relates to an image forming apparatus.
In a conventional image forming device of an electric photography type such as a printer, a copier, and a facsimile, a charge roller charges a surface of a photosensitive drum. An exposure device exposes the photosensitive drum to form a static latent image thereon. A developing device develops the static latent image to form a toner image. A transfer roller transfers the toner image to a sheet. A cleaning device removes toner remaining on the photosensitive drum after the transfer roller transfers the toner image.
In a non-contact type charge device disclosed in Patent Reference 1, a charge roller includes a metal shaft and an elastic layer formed of a conductive rubber and disposed on the metal shaft. A resin coating layer and a surface modified layer are disposed on the elastic layer. The charge roller is arranged close to a photosensitive drum. A voltage is applied to the charge roller, so that the charge roller charges a surface of the photosensitive drum.
In the conventional non-contact type charge device, pressing members are disposed at both ends of a shaft of the charge roller, so that the charge roller is pressed against the photosensitive drum. Further, gap setting members are disposed on an elastic layer of the charge roller at both ends thereof for forming a gap between the charge roller and the photosensitive drum.
Patent Reference 1: Japanese Patent Publication No. 2001-350321
In the conventional non-contact type charge device, the pressing members are disposed at both ends of the shaft of the charge roller, so that the charge roller is pressed against the photosensitive drum. Accordingly, the charge roller may be deformed due to the pressing force. In this case, the gap becomes large at a center portion of the charge roller, and decreases toward the both ends thereof. Further, when the shaft has a smaller diameter, an extent of the deformation increases. As a result, it is difficult to form a constant gap between the charge roller and the photosensitive drum, thereby making it difficult to consistently charge the photosensitive drum.
In order to form a constant gap, the charge roller may be formed in a crown shape with high precision. In this case, it takes long time to machine the charge roller, thereby increasing cost of an image forming apparatus. Alternatively, the shaft may have a large diameter. In this case, the charge roller has a large outer diameter, thereby increasing a size of an image forming apparatus.
In view of the problems described above, an object of the present invention is to provide an image forming apparatus, in which it is possible to form a constant gap between a charge roller and a photosensitive drum with low cost configuration, thereby making it possible to consistently charge the photosensitive drum.
Further objects and advantages of the invention will be apparent from the following description of the invention.